WO2013135002A1

WO2013135002A1 - Method for preparing composite substrate for gan growth

Info

Publication number: WO2013135002A1
Application number: PCT/CN2012/075856
Authority: WO
Inventors: 孙永健; 张国义; 童玉珍
Original assignee: 东莞市中镓半导体科技有限公司
Priority date: 2012-03-14
Filing date: 2012-05-22
Publication date: 2013-09-19
Also published as: EP2826892A1; EP2826892B1; EP2826892A4; JP6091530B2; US20140357053A1; JP2015518265A; KR20140097364A; CN103305909A; CN103305909B; KR101636721B1

Abstract

Disclosed in the present invention is a method for preparing a composite substrate for GaN growth. The method comprises: first growing a GaN monocrystal epitaxial layer on a sapphire substrate, then bonding the GaN epitaxial layer onto a temporary substrate with an epoxy-type instant adhesive, lifting off the sapphire substrate by laser, then bonding the GaN epitaxial layer on the temporary substrate with a thermally and electrically conducting substrate, shedding the temporary substrate, and so obtaining the composite substrate in which the GaN layer of face-up gallium polarity is bonded to the thermally and electrically conducting substrate. When the GaN layer on the sapphire substrate is directly bonded to the thermally and electrically conducting substrate and the sapphire substrate is lifted off by laser, a composite substrate in which a GaN epitaxial sheet of face-up nitrogen polarity is bonded to the thermally and electrically conducting substrate is obtained. The composite substrate prepared in the present invention not only has homoepitaxy and improves the quality of crystals but also can be used directly for the preparation of LEDs with a vertical structure, and merely uses a thin layer of GaN monocrystal, greatly reducing costs and possessing advantages in applications.

Description

Method for preparing composite substrate for GaN growth

The present invention relates to the field of semiconductor optoelectronic devices and metal organic chemical vapor deposition (MOCVD) technology, and more particularly to a method of fabricating a composite substrate for growing GaN epitaxial wafers. Background technique

III/V nitrides dominated by GaN and InGaN and AlGaN are semiconductor materials of recent interest, with a 1.9-6.2 eV continuously variable direct band gap, excellent physical and chemical stability, and high saturation electron mobility. Etc. characteristics make it the most preferred material for optoelectronic devices such as lasers, light-emitting diodes, and the like.

However, for the current GaN-based semiconductor material devices, the epitaxial film of the GaN-based LED is generally grown on a substrate such as sapphire substrate, SiC, Si or the like due to the lack of a GaN substrate. Up to now, the epitaxial growth technology of GaN material systems is basically based on heterogeneous heteroepitaxial technology. The most widely used, patent-protected, mainly heteroepitaxial technology for sapphire substrates. The main problems are: 1. Due to the large lattice mismatch and thermal stress mismatch between GaN and sapphire, the misfit dislocation of 10 ⁹ cm _ ² is caused, which seriously affects the crystal quality and reduces the luminous efficiency of the LED. And the service life; 2. Sapphire is an insulator. The resistivity at room temperature is greater than lO^Q cm, so that it is impossible to fabricate a vertical structure. Usually, N-type and P-type electrodes can be fabricated on the upper surface of the epitaxial layer, thus making the effective light-emitting area Reducing, at the same time increasing the lithography and etching process in device fabrication, reducing the utilization of materials; 3. The thermal conductivity of sapphire is not good, the thermal conductivity at 100 ^Q C is about 0.25 W/cm K, which The performance of GaN-based devices has a great impact. Especially in large-area high-power devices, the heat dissipation problem is very prominent. 4. In the fabrication of GaN-based lasers (LD), the sapphire hardness is very high, and there is a 30 degree between the sapphire crystal lattice and the GaN crystal lattice. The angle is so that it is difficult to obtain the cleavage plane of the epitaxial layer of InGaN LD, and the cavity surface of InGaN-LD cannot be obtained by cleavage.

For the SiC substrate, although the crystal constant is the closest to the GaN lattice constant and the lattice mismatch is small, it is also heteroepitaxial, and there are also misfit dislocations and thermal misfit dislocations, and SiC lining. The bottom cost is expensive and there are significant difficulties in the application of GaN-based LED devices. The Si substrate is also a GaN-based epitaxial substrate that has been studied in recent years. However, the lattice mismatch of Si substrate and GaN is larger than that of sapphire substrate, and the Si substrate is cubic crystal orientation, and GaN is hexagonal crystal. This increases the difficulty of epitaxial GaN material on it. At present, the GaN layer grown on the Si substrate faces serious problems such as cracking, and the growth thickness is hard to exceed 4 μm.

Therefore, for crystal epitaxy, no matter from the theoretical theory of epitaxial growth or the development history of semiconductor epitaxial technology, It has been proven that homogenous extension is the best choice. Recently, people began to develop GaN single crystal substrate preparation technology, the emergence of GaN single crystal substrate, GaN epitaxial regression of homoepitaxial growth, can improve the crystal quality of epitaxial GaN crystal, and better thermal conductivity of GaN crystal The conductive characteristics enable LED epitaxial wafers epitaxially grown using GaN substrates to be directly fabricated into vertical structure LED devices, thereby improving the performance of the device under high current injection. However, the high price of GaN single crystal substrates directly limits its application in LED devices. At present, the price of a 2-inch GaN single crystal substrate can reach 2,000 US dollars. At present, the price of a 2-inch high-power LED epitaxial wafer is less than 100 US dollars. This huge cost completely limits the GaN single crystal substrate in the LED market. application. Summary of the invention

The object of the present invention is to provide a novel composite substrate for growing a GaN epitaxial wafer and a preparation method thereof, which are required to take into consideration the homoepitaxial requirements required for GaN epitaxy, improve crystal quality, and directly prepare vertical Structure LEDs, and reduce production costs, so that they can be put into practical use.

The composite substrate for GaN growth proposed by the present invention, as shown in Fig. 1, comprises a thermally conductive layer 1 and a GaN single crystal layer 2 on the thermally conductive layer.

The above thermally conductive layer has a thickness of from 10 μm to 3000 μm, preferably from 50 μm to 400 μm. The material of the thermally conductive layer needs to satisfy several characteristics. (1) The melting point exceeds 1000 ° C, or it can remain substantially solid at 1000 ° C; (2) It has high thermal conductivity and electrical conductivity.

According to the above requirements, the material of the thermally conductive layer may be selected from elemental metals or alloys or quasi-alloys, such as metal W, metal M, metal Mo, metal Pd, metal Au, metal Cr, etc., or any two or two of the above metals. More than one alloy, or an alloy of one or more of the above metals and Cu, such as WCu alloy, MoCu alloy, and MCu alloy. In addition to the metal, the material of the thermally conductive layer may be a Si crystal, a SiC crystal or an AlSi crystal or the like.

The thickness of the GaN layer on the thermally conductive layer is from 0.1 μm to 100 μm, preferably from 1 μm to 50 μm. The GaN layer exists in a single crystal form.

The thermally conductive conductive layer and the GaN single crystal layer may be connected by rigid or flexible bonding. If the bond is a rigid van der Waals force bond, the thermal expansion coefficient of the material of the thermally conductive conductive layer is required to be close to that of GaN, where the similarity means that the thermal expansion coefficient is within 10%, and the thermally conductive material and GaN are conductive. There is no medium between the crystals. The thermally conductive layer can also be bonded to the GaN layer by a flexible medium. In the case of flexible media bonding, the media is required to have a temperature of more than 1000 °. The melting point, and a certain ductility, can relax the stress, preferably with AuAu bonding of 0.5 micron to 5 micron thickness, or high temperature metal bonding of metal W, Pd or Ni. The metal dielectric bonding layer having the above thickness can relax the thermal mismatch stress between the GaN and the thermally conductive conductive layer due to the difference in thermal expansion coefficient, and therefore, using a flexible dielectric bond In this way, the thermal expansion coefficient of the thermally conductive layer is not required to be the same as or similar to GaN.

Further, the composite substrate of the present invention further has a reflective layer located inside, bottom or bottom surface of the GaN single crystal layer, and the bottom surface of the GaN single crystal layer is connected to the thermally conductive conductive layer of the GaN single crystal layer. one side. The reflective layer may be located at one end of the bonding layer between the thermally conductive layer and the GaN layer (ie, between the bonding layer and the GaN layer), as shown in FIG. 2, or may be located inside or at the bottom of the GaN layer, such as Figure 3 shows. If the reflective layer is located at one end of the bonding layer adjacent to the GaN layer, the reflective layer may be a metal reflective layer such as a metal reflective layer such as Pd, Cr. If the reflective layer is located inside the GaN layer or at the bottom of the GaN layer, the reflective layer may be a periodic or quasi-periodic structure having a grating or photonic lattice structure, as shown in FIG.

The grating structure refers to a micron-scale periodic structure, and the photonic lattice structure refers to a nano-scale periodic structure, which may be periodic conical protrusions or pits, truncated protrusions or pits. , cylindrical protrusions or dimples, triangular pyramidal protrusions or dimples, or other periodic protrusions or dimples of any shape. As shown in Fig. 5, (a) shows a periodic structure of a triangular pyramid pit, and (b) shows a periodic structure of a cylindrical pit. The microstructural period of the micron- or nano-scale periodic structure may be from 10 nm to 50 μm, preferably from 200 nm to 10 μm. In Figure 5, w and d represent the maximum width and depth of the pit, respectively, and A represents the structural period, where A > w.

The micron- or nano-scale periodic structure as a reflective layer is usually made of a material that can withstand high temperature (melting point over 1000 ° C) and can be grown in a crystal form, for example, a periodic structure formed of a material such as SiO ₂ or SiN. Embedded in the GaN single crystal layer, these materials and GaN have different refractive indices, thus forming an effective total reflection interface, and the periodic structure effectively increases the average refractive index of the interface.

In some cases, the periodic structure at the bottom of the GaN layer is not formed of a material different from GaN, but only a periodic pattern formed on the bottom surface of the GaN layer, and such a periodic pattern can also function as a reflective layer.

The reflective layer has a very important effect on GaN-based devices epitaxially grown using the composite substrate of the present invention. Generally, in a light-emitting device epitaxially grown on a substrate, the active layer emits light to 360 degrees. Without the design of the reflective layer, nearly 40% of the light emitted from the light-emitting material in the direction of the conductive layer is absorbed by the substrate and cannot be emitted. Therefore, the use of a composite substrate with a reflective layer design can increase the light extraction efficiency by at least 30%. The composite substrate of the present invention can be directly used for epitaxial growth of GaN epitaxial wafers, and further to prepare vertical structure LED devices. Compared with traditional technology, it has very obvious advantages.

First, the growth of the prior art sapphire substrate is compared. Nowadays, the sapphire substrate is the most commonly used substrate for GaN epitaxial wafer growth. Since the sapphire substrate is non-conductive and non-conductive, it is difficult to prepare vertical structure LED devices for GaN grown on sapphire substrates, and most of them are prepared as planar structure LEDs, which is not conducive to heat dissipation. Unable to prepare for high power devices. In addition, sapphire substrate Due to the heterogeneous substrate with GaN, the growth quality of GaN is limited, and high-quality GaN epitaxial wafers cannot be prepared.

The composite substrate of the present invention has significant advantages over sapphire substrates. On the one hand, the composite substrate has a GaN layer. Therefore, the GaN epitaxial wafer grown on the composite substrate belongs to homoepitaxial growth, which can significantly improve the crystal quality of the grown GaN epitaxial wafer, thereby improving the internal quantum efficiency. On the other hand, the use of the thermally conductive layer in the composite substrate allows the GaN epitaxial wafer grown by the composite substrate to be directly fabricated into a vertical structure LED device according to the conventional chip process, without being restricted by the substrate being unable to conduct heat conduction and conduction, and Limits increase the efficiency of the device.

Second, Si substrate growth and SiC substrate growth relative to the prior art. Although the two kinds of substrates can directly prepare vertical structure LEDs due to their thermal conductivity, the GaN epitaxial wafers grown thereon are heteroepitaxial, which is unfavorable for the quality of the grown GaN crystal. Especially for Si substrates, the GaN epitaxial growth thereon requires the insertion of a plurality of layers of AlGaN to adjust the stress, and the thickness of GaN grown thereon is hard to exceed 3-4 μm. Although the SiC substrate is similar to the GaN crystal lattice constant, it is difficult to be widely used in GaN-based high-power LED devices because the SiC crystal itself is very difficult to fabricate and expensive. The main advantage of the composite substrate of the present invention relative to the two substrates is that the composite substrate belongs to homoepitaxial growth, which can improve the crystal quality of the GaN epitaxial wafer and obtain a wider application.

Finally, the GaN single crystal substrate is a homoepitaxial substrate with respect to the GaN single crystal substrate, and is homogenously epitaxial with the composite substrate of the present invention, and the epitaxial growth of the two substrates can be greatly improved. GaN crystal quality. However, compared with the high cost of the GaN single crystal substrate, the composite substrate of the present invention uses a heat conductive conductive material which is less expensive as a raw material and has a thickness of only one to one quarter of GaN of a GaN single crystal substrate. The layer, the price is much lower than the GaN single crystal substrate, so it has a broader application prospect. In order to prepare the above composite substrate for GaN growth, the present invention proposes two preparation methods for preparing a composite substrate having a gallium polar face up and a nitrogen polar face up.

The first method for preparing a composite substrate with a gallium polarity facing up includes the following steps:

La) growing a GaN single crystal epitaxial layer on a sapphire substrate;

Lb) bonding the GaN epitaxial wafer grown on the sapphire substrate to a temporary substrate by epoxy-based quick-drying adhesive, and then peeling off the sapphire substrate by laser lift-off method;

Lc) bonding the GaN epitaxial wafer bonded to the temporary substrate to a thermally conductive substrate having a melting point of more than 1000 ° C, and the epoxy-based quick-drying adhesive is carbonized during the bonding process, and the temporary substrate is peeled off. After surface cleaning, a composite substrate in which a GaN epitaxial wafer with a gallium polarity face up and a thermally conductive conductive substrate are bonded together is obtained.

In the above step la), the growth method of GaN can be grown by a MOCVD method or an HVPE method well known to those skilled in the art, or a combination of the MOCVD method and the HVPE method. Usually use MOCVD first The method is followed by growing a GaN single crystal using an HVPE (Hydride Vapor Phase Epitaxy) method.

The sapphire substrate may be a flat sapphire substrate or a patterned sapphire substrate. The patterned sapphire substrate is designed according to the structure of the reflective layer in the composite substrate, and a micron- or nano-scale periodic structure pattern is prepared on the sapphire surface by a photolithographic stripping method well known to those skilled in the art. For a GaN single crystal layer grown using a patterned sapphire substrate and transferred onto a temporary substrate, the pattern of the sapphire substrate is successfully transferred to the GaN layer upon peeling, and the pattern can be used as a reflective layer. For a GaN single crystal layer grown using a flat sapphire substrate, the reflective layer can be prepared by one of two methods:

I. After transferring the GaN single crystal layer from the sapphire substrate onto the temporary substrate in step lb), a metal reflective layer is deposited on the surface of the GaN single crystal by an evaporation technique well known to those skilled in the art (the thickness is usually 1 Within micron), then proceed to step lc). The metal reflective layer is located on the underside of the GaN single crystal layer in the finally obtained composite substrate with the gallium polarity facing upward.

II. In the process of performing GaN epitaxial growth in step la), a layer of GaN is grown, and then a reflective layer material is grown thereon, which is performed by photolithography and dry etching methods well known to those skilled in the art. The layer of reflective layer material is prepared as a micron or nanoscale periodic structure (ie, a reflective layer structure), and it is required to expose the GaN surface at the gaps of these structures, and then continue to grow the GaN single crystal to a desired thickness, and then proceed to step lb) . In the finally produced composite substrate with a gallium polarity facing up, the reflective layer structure is located inside the GaN layer. .

In the above method II, the reflective layer material is required to have a refractive index different from that of GaN, and the melting point reaches 1000 ° C or higher, and may be grown by crystal growth or coating, such as SiO ₂ and SiN. The Si0 ₂ layer or the SiN layer can be grown by a PECVD method (plasma enhanced chemical vapor deposition method) to a thickness of 0.2 μm to 2 μm.

The epoxy-based quick-drying adhesive such as 502 adhesive in the above step lb); the temporary substrate such as a metal temporary substrate or a Si single crystal temporary substrate.

The bonding method in the above step lc) may be a rigid or flexible medium bonding. The so-called rigid bonding is carried out by van der Waals force without any evaporation of the bonding metal, at a temperature of 500 ° C to 900 ° C, a pressure of 3 ton / square inch to 10 ton / square inch, The GaN epitaxial wafer bonded to the temporary substrate is directly bonded to the thermally conductive substrate by van der Waals. As described above, the rigid bonding requires that the thermally conductive layer substrate material and the GaN have a thermal expansion coefficient within 10%, such as a Si single crystal substrate, a SiC single crystal substrate, an AlSi crystal substrate or the like.

The so-called flexible medium bonding is to deposit the bonding metal on the surface to be bonded, and then bond to the temporary lining at a temperature of 200 ° C to 900 ° C and a pressure of 1 ton / square inch to 5 ton / square inch. The GaN epitaxial wafer on the bottom is bonded to the thermally conductive substrate. The thickness of the bonding layer of the flexible medium bonding is preferably 0.5 μm to 5 μm, and the bonding metal is, for example, Au, W, Pd and M, etc. The second method of preparing a composite substrate with a nitrogen polarity facing up includes the following steps:

2a) growing a GaN single crystal epitaxial layer on a sapphire substrate;

2b) bonding the epitaxial wafer grown on the sapphire substrate to a thermally conductive substrate having a melting point exceeding 1000 ° C;

2c) The sapphire substrate is peeled off by a laser lift-off method to obtain a composite substrate in which a GaN epitaxial wafer having a nitrogen polarity facing upward is bonded to a thermally conductive substrate.

In the above step 2a), the growth method of GaN can be grown by a MOCVD method or an HVPE method well known to those skilled in the art, or a combination of the MOCVD method and the HVPE method. Usually, the CVD method is used to grow GaN single crystals using the HVPE method.

The GaN single crystal epitaxial layer of step 2a) is grown on a flat sapphire substrate. For a composite substrate designed with a reflective layer, the reflective layer can be prepared by one of the following two methods before performing step 2b):

A. A metal reflective layer (typically within 1 micron in thickness) is deposited on the surface of the GaN single crystal prepared in step 2a) by an evaporation technique well known to those skilled in the art, and then subjected to step 2b). In the finally prepared composite substrate having a nitrogen polarity facing up, the metal reflective layer is located on the bottom surface of the GaN single crystal layer.

B. In the process of performing GaN epitaxial growth in step 2a), a layer of GaN is grown, and then a layer of reflective layer material is grown thereon, which is performed by photolithography and dry etching methods well known to those skilled in the art. The layer reflective layer material is prepared as a micron- or nano-scale periodic structure (ie, a reflective layer structure), and it is required to expose the GaN surface at the gaps of these structures, and then continue to grow the GaN single crystal to a desired thickness, and then proceed to step 2b) . In the finally produced composite substrate with the nitrogen polarity facing up, the reflective layer structure is located inside the GaN layer.

In the above method B, the reflective layer material is required to have a refractive index different from that of GaN, and the melting point is 1000 ° C or higher, and may be grown by crystal growth or plating, such as SiO ₂ and SiN. The Si0 ₂ layer or the SiN layer can be grown by a PECVD method (plasma enhanced chemical vapor deposition method) to a thickness of 0.2 μm to 2 μm.

The bonding method in the above step 2b) can be performed by rigid or flexible medium bonding. The so-called rigid bond is the sapphire in the case of not depositing any bonding metal, by van der Waals force, at a temperature of 500 ° C to 900 ° C, a pressure of 3 ton / square inch to 10 ton / square inch The GaN epitaxial wafer on the substrate is directly bonded to the thermally conductive substrate by van der Waals. As described above, the rigid bonding requires that the thermal conductive layer substrate material and the GaN have a thermal expansion coefficient within 10%, such as a Si single crystal substrate, a SiC single crystal substrate, an AlSi crystal substrate or the like.

The so-called flexible medium bonding is to deposit the bonding metal on the surface to be bonded, and then epitaxy of GaN on the sapphire substrate at 200 ° C to 900 ° C, pressure 1 ton / square inch to 5 ton / square inch The sheet is bonded to a thermally conductive substrate. The thickness of the bonding layer of the flexible medium bonding is preferably from 0.5 μm to 5 μm, and a bonding metal such as Au, W, Pd, Ni, or the like. In summary, the present invention utilizes a laser lift-off technique, a bonding technique, a micro-machining technique, and an epitaxial technique to prepare a novel composite substrate, which not only takes into account the homoepitaxial extension required for GaN epitaxy, but also improves the crystal quality. The vertical structure LED is directly prepared, and since only a thin layer of GaN single crystal is used, the cost is greatly reduced, making it an advantage in the existing GaN material substrate. DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view showing the basic structure of a composite substrate for growing GaN of the present invention.

2 is a schematic view showing the structure of a composite substrate in which a reflective layer is located adjacent to a GaN-end of a composite substrate bonding layer.

3 is a schematic view showing the structure of a composite substrate in which a reflective layer is located in a GaN layer of a composite substrate.

4 is a schematic diagram of a periodic structure of a reflective layer grating or a photonic lattice.

Fig. 5 is a schematic view showing the periodic structure in which the reflective layer is in the shape of a triangular pyramid pit (a) or a cylindrical pit (b).

Fig. 6 is a view showing the steps of the second step of the first embodiment of the present invention, in which the Si substrate is bonded by 502 and the sapphire substrate is laser-peeled. Fig. 7 is a view showing the steps of the third step of the high temperature bonding and the high temperature dropping of the Si substrate in the first embodiment.

8 is a flow chart of fabricating a GaN/WCu composite substrate having a reflective layer structure in a GaN layer in Example 2, wherein: (a) is a second step of preparing Si0 ₂ periodic reflection on a GaN surface of a 4 micron GaN/sapphire substrate. (b) is a schematic diagram of the third step of making a reflective layer and then continuing to grow GaN to GaN to a total thickness of 10 μm by using HVPE technology; (c) is a fourth step of processing to obtain a reflection on the Si substrate. Schematic diagram of the GaN layer structure of the layer structure; (d) is a schematic structural view of the finally obtained GaN/WCu composite substrate.

9 is a flow chart of fabricating a GaN/MoCu composite substrate having a metal reflective layer in Example 4, wherein: (a) is a third step of vapor-depositing a Pd metal reflection on a GaN single crystal layer bonded to a Si substrate. A schematic view of the structure obtained by the layer; (b) is a schematic structural view of a GaN/MoCu composite substrate having a Pd metal reflective layer obtained by NiNi bonding.

10 is a flow chart of a composite substrate for fabricating a Si substrate van der Waals bonded GaN layer in Embodiment 5, wherein: (a) is a third step of preparing a Si0 ₂ cylindrical period on a GaN surface of a GaN/sapphire substrate. Schematic diagram of the structure; (b) is the fourth step of the HVPE technology to continue to grow GaN to GaN to a total thickness of 50 microns after the formation of the reflective layer; (c) is the fifth step through van der Waals bonding to form sapphire / GaN / Schematic diagram of the Si structure; (d) is a schematic diagram of the sixth step of obtaining a GaN/Si composite substrate by laser lift-off.

11 is a flow chart of fabricating a composite substrate of an AlSi-lined AuAu-bonded GaN layer in Example 7, wherein: (a) is a schematic view of the third step of preparing a Si0 ₂ cylindrical periodic structure on a GaN surface of a GaN/sapphire substrate; (b) is the fourth step A schematic diagram of continuing to grow GaN to GaN to a total thickness of 10 μm using HVPE technology as a reflective layer; (c) is a schematic diagram of forming a sapphire/GaN/AISi structure by AuAu bonding in the fifth step; (d) is a sixth step by laser A schematic of the GaN/AISi composite substrate obtained by stripping.

Figure 12 is a photograph of a composite substrate in which a GaN single crystal layer prepared by the present invention is bonded to a metal substrate.

In the picture:

1 thermal conductive layer, 2 - GaN layer, 3 - bonding layer, 4 - reflective layer, 4 ' a reflective layer pattern structure, 5 - sapphire substrate, 6 - Si substrate, 7 - AlSi single crystal substrate. detailed description

The present invention will be described in detail below with reference to the accompanying drawings, but this is not to be construed as a limitation of the invention. Ideas are within the scope of the invention.

Example 1 : WCu metal substrate AuAu bonded GaN layer non-reflective layer metal composite substrate

In the first step, a 2 inch thick GaN single crystal epitaxial wafer is grown using a 2 inch 430 micron thick flat sapphire substrate by MOCVD techniques well known to those skilled in the art, followed by growth using HVPE techniques well known to those skilled in the art. The total thickness of GaN to GaN single crystals reaches 10 microns.

In the second step, the GaN surface of the above-mentioned grown GaN single crystal is bonded to a 2-inch 400-micron-thick single crystal Si substrate using 502 fast-drying glue, and the Si substrate is used as a transfer supporting substrate, and then passed through the field. The laser lift-off technique well known to the skilled person strips off the sapphire substrate leaving only the GaN single crystal bonded to the Si substrate, as shown in FIG.

In the third step, 1 μm of Au was vapor-deposited simultaneously on the GaN surface of the GaN single crystal on the Si substrate and the surface of the WCu alloy substrate, and then bonded together at 300 ° C under a pressure of 5 tons for 15 minutes. After the bonding is completed, the 502 quick-drying adhesive is carbonized at a high temperature, so that the connection between the Si substrate and the GaN/WCu composite substrate is automatically separated.

Finally, a GaN/WCu composite substrate is obtained by surface cleaning. The substrate comprises a 150 μm thick WCu alloy metal substrate, and the mass ratio of W to Cu is 15% to 85%. The WCu alloy metal substrate was bonded by AuAu bonding and a layer of 10 μm thick GaN single crystal, and the bonding layer Au was 2 μm thick. Example 2: WCu metal substrate AuAu bonded metal composite substrate of GaN layer

In the first step, a 4 micron thick GaN single crystal epitaxial wafer was grown using a 2 inch 430 micron thick flat sapphire substrate using MOCVD techniques well known to those skilled in the art.

In the second step, a 1 micron thick SiO ₂ film is grown on the surface of the grown GaN single crystal by PECVD. The thin layer of SiO _{2 is} prepared into a conical periodic structure having a period of 3 μm, a bottom diameter of 2.5 μm and a height of 1 μm by photolithography and dry etching techniques well known to those skilled in the art, as shown in Fig. 8 (a). Show. The GaN surface is exposed at the pitch of the conical pattern. This periodic structure can be used as a reflective layer.

In the third step, the GaN single crystal surface on which the reflective layer structure is prepared is continuously grown to a total thickness of 10 μm using a HVPE technique well known to those skilled in the art, as shown in Fig. 8(b).

In the fourth step, the GaN surface of the above-mentioned well-grown GaN single crystal is bonded to a 2-inch 400-micron single crystal Si substrate using 502 fast-drying adhesive, and the Si substrate is used as a transfer supporting substrate, and then through the prior art. The laser lift-off technique known to the person peels off the sapphire substrate, leaving only the GaN single crystal bonded to the Si substrate, as shown in Fig. 8(c).

In the fifth step, 1 μm of Au was vapor-deposited simultaneously on the GaN surface of the GaN single crystal on the Si substrate and the surface of the WCu alloy substrate, and then bonded together at 300 ° C under a pressure of 5 tons for 15 minutes. After the bonding is completed, the 502 quick-drying adhesive is carbonized at a high temperature, so the connection between the Si substrate and the GaN/WCu composite substrate is automatically separated (see Fig. 7).

Finally, a composite substrate as shown in Fig. 8(d) is obtained by surface cleaning, and the substrate comprises a 150 μm thick WCu alloy metal substrate 1, and the mass ratio of W and P Cu is 15% to 85%. The bonding layer 3 was bonded to a thickness of 2 μm by AuAu bonding and a layer of 10 μm thick GaN single crystal layer 2. A reflective layer pattern 4' is formed in the GaN layer 2 near the bonding layer 4 microns, and the pattern is a conical SiO ₂ pattern layer structure having a period of 3 μm, a height of 1 μm, and a bottom diameter of 2.5 μm. Example 3: Metal composite substrate of AuCu bonded GaN layer on MoCu metal substrate

In the second step, a 1 μm thick SiO ₂ film is grown on the surface of the grown GaN single crystal by PECVD, and a thin layer of SiO _{2 is} prepared by photolithography and dry etching techniques well known to those skilled in the art. A conical periodic structure with a period of 3 microns, a bottom diameter of 2.5 microns, and a height of 1 micron, see Figure 8(a). The GaN surface is exposed at the pitch of the conical pattern. This periodic structure can be used as a reflective layer.

In the third step, the GaN single crystal surface on which the reflective layer structure is prepared is continuously grown using a HVPE technique well known to those skilled in the art to a total thickness of GaN to GaN single crystal of 10 μm, see 8 (b).

In the fourth step, the GaN surface of the above-mentioned well-grown GaN single crystal is bonded to a 2-inch 400-micron single crystal Si substrate using 502 fast-drying adhesive, and the Si substrate is used as a transfer supporting substrate, and then through the prior art. The laser lift-off technique known to the person strips off the sapphire substrate, leaving only the GaN single crystal bonded to the Si substrate, see Figure 8(c).

In the fifth step, the GaN surface of the GaN single crystal on the Si substrate and the surface of the MoCu alloy substrate are simultaneously vapor-deposited by 1 μm. Au, then bonded together at 15 ° C for 5 minutes at 300 ° C. After the bonding is completed, the 502 quick-drying adhesive is carbonized at a high temperature, and therefore, the connection between the Si substrate and the GaN/MoCu composite substrate is automatically separated.

Finally, a GaN/MoCu composite substrate was obtained by surface cleaning. The substrate comprises a 150 μm thick MoCu alloy metal substrate, and the mass ratio of Mo to Cu was 20% to 80%. The MoCu alloy metal substrate was bonded by AuAu bonding and a layer of 10 μm thick GaN single crystal, and the bonding layer Au was 2 μm thick. A layer of reflective layer pattern is included in the GaN layer adjacent to the bonding layer 4 microns. The pattern is a conical SiO ₂ pattern layer structure with a period of 3 micrometers, a height of 1 micrometer, and a bottom diameter of 2.5 micrometers. Example 4: MoCu metal substrate NiNi bonded GaN layer metal composite substrate

In the second step, the GaN surface of the above-mentioned well-grown GaN single crystal is bonded to a 2-inch 400-micron single crystal Si substrate using a 502 fast-drying adhesive, and the Si substrate is used as a transfer supporting substrate, and then through the prior art. The laser lift-off technique known to the person peels off the sapphire substrate, leaving only the GaN single crystal bonded to the Si substrate.

In the third step, 200 nm of Pd metal is deposited as a reflective layer 4 on the GaN surface of the GaN single crystal layer 2 on the Si substrate 6, as shown in Fig. 9 (a).

In the fourth step, the GaN single crystal on the Si substrate on which the reflective layer is vapor-deposited is simultaneously vapor-deposited on the reflective layer and the surface of the MoCu alloy substrate by 2 μm of Ni, and then passed through at 800 ° C under a pressure of 15 tons. Bond together in 15 minutes. After the bonding is completed, the 502 quick-drying adhesive is carbonized at a high temperature, so that the connection between the Si substrate and the GaN/MoCu composite substrate is automatically separated.

Finally, by surface cleaning, a composite substrate as shown in Fig. 9(b) was obtained, which substrate comprises a 150 μm thick MoCu alloy metal substrate 1, and the mass ratio of Mo and Cu was 20% to 80%. The MoCu alloy metal substrate 1 is bonded by NiNi bonding and a layer of 4 μm thick GaN single crystal layer 2, the bonding layer 3 having a thickness of 4 μm, including a layer adjacent to the bonding layer 3 of the GaN layer 2 Layer Pd metal reflective layer 4. Example 5: Composite substrate of a GaN layer bonded to a van der Waals bonded Si substrate

In the second step, the above GaN single crystal is continuously grown to a total thickness of 46 μm from GaN to GaN using a HVPE technique well known to those skilled in the art.

In the third step, a 1 micron thick SiO ₂ film is grown on the surface of the GaN single crystal grown by PECVD. The thin layer of SiO _{2 is} prepared into a cylindrical periodic structure having a period of 3 μm, a bottom diameter of 2 μm and a height of 1 μm by photolithography and dry etching techniques well known to those skilled in the art, as shown in Fig. 10 (a). Show. The GaN surface is exposed at the pitch of the cylindrical pattern. This periodic structure can be used as a reflective layer.

In the fourth step, the above GaN single crystal in which the reflective layer structure is prepared is continuously grown using HVPE technology. The total thickness of the GaN to GaN single crystal is 50 μm, as shown in Fig. 10 (b).

In the fifth step, the prepared GaN crystal having a reflective layer structure and a 400 micron thick Si wafer are bonded together at a temperature of 900 ° C under a pressure of 20 tons for 30 minutes by direct van der Waals bonding to form sapphire/ A structural sample such as GaN/Si is shown in Figure 10 (c).

In the sixth step, the sapphire substrate is stripped off by laser lift-off techniques well known to those skilled in the art, leaving only the GaN/Si bonded composite substrate structure, as shown in Figure 10(d).

Finally, by surface cleaning, a composite substrate as shown in Fig. 10(d) is obtained, which comprises a 400 μm thick Si single crystal substrate 6, bonded by van der Waals force and a layer of 50 μm thick. The GaN single crystal layer 2 is bonded together. The reflective layer pattern 4' is formed at a depth of 4 micrometers near the bonding surface of the GaN layer 2. The reflective layer pattern 4' has a period of 3 micrometers, a height of 1 micrometer, and a bottom-bottom diameter of 2 micrometers of a cylindrical Si0 ₂ pattern layer structure. . Example 6: Metal composite substrate of SiC substrate PdPd bonded GaN layer

In the second step, a 1 μm thick SiO ₂ film is grown on the surface of the grown GaN single crystal by PECVD, and a thin layer of SiO _{2 is} prepared by photolithography and dry etching techniques well known to those skilled in the art. A conical periodic structure with a period of 3 microns, a bottom diameter of 2.5 microns, and a height of 1 micron, see Figure 8(a). The GaN surface is exposed at the pitch of the conical pattern. This periodic structure can be used as a reflective layer

In the third step, the above GaN single crystal in which the reflective layer structure is prepared is continuously grown to a total thickness of 10 μm using HVPE technology well known to those skilled in the art, as shown in Fig. 8 (b).

In the fourth step, the GaN face of the above-mentioned grown GaN single crystal was bonded to a 2-inch 400-micron single crystal Si substrate using a 502 quick-drying adhesive, and a Si substrate was used as a transfer supporting substrate. The sapphire substrate is then stripped off by laser lift-off techniques well known to those skilled in the art, leaving only the GaN single crystal bonded to the Si substrate, see Figure 8(c).

In the fifth step, 1 μm of Pd was simultaneously evaporated on the GaN surface of the GaN single crystal on the Si substrate and the surface of the SiC substrate of 200 μm thick. It was then bonded together at 800 ° C under a pressure of 8 tons over 15 minutes. After the bonding is completed, the 502 quick-drying glue is carbonized at a high temperature, and therefore, the connection between the Si substrate and the GaN/SiC composite substrate is automatically separated. Finally, a composite substrate having the structure shown in FIG. 8(d) can be obtained by surface cleaning, except that the WCu alloy metal substrate of Example 2 is replaced by a 200 μm thick SiC single crystal substrate, which is SiC single crystal lining. The bottom is bonded by a PdPd bond to a 10 micron thick GaN single crystal. The bonding layer Pd has a thickness of 2 μm. The GaN layer includes a reflective layer pattern structure near the bonding layer 4 micrometers. The reflective layer pattern structure is a conical SiO ₂ pattern layer structure having a period of 3 micrometers, a height of 1 micrometer, and a bottom diameter of 2.5 micrometers. Example 7: Composite substrate of AuSi substrate AuAu bonded GaN layer

In the first step, a 6-inch thick GaN single crystal epitaxial wafer was grown using a 2 inch 430 micron thick flat sapphire substrate using MOCVD techniques well known to those skilled in the art.

In the third step, a 1 micron thick SiO ₂ film is grown on the surface of the above grown GaN single crystal by PECVD, and a thin layer of SiO _{2 is} prepared by photolithography and dry etching techniques well known to those skilled in the art. A cylindrical periodic structure with a period of 3 μm, a bottom diameter of 2 μm and a height of 1 μm is shown in Fig. 11 (a). The GaN surface is exposed at the pitch of the cylindrical pattern. This periodic structure can be used as a reflective layer.

In the fourth step, the above GaN single crystal in which the reflective layer structure is prepared is continuously grown to a total thickness of 10 μm using HVPE technology well known to those skilled in the art, as shown in Fig. 11 (b). .

In the fifth step, 1 μm of Au was vapor-deposited simultaneously on the GaN surface of the sapphire/GaN single crystal and the surface of the 200 μm thick AlSi substrate. Then, at 300 ° C, pressure 5 tons, press together for 15 minutes, as shown in Figure 11 (c).

In the sixth step, the sapphire substrate is stripped off by laser lift-off techniques well known to those skilled in the art, leaving only the GaN/AISi bonded composite substrate structure, as shown in Figure 11(d).

Finally, a composite substrate as shown in Fig. 11 (d) was obtained by surface cleaning, and the substrate included a 200 μm thick AlSi single crystal substrate 7 having an Al composition of 30% and a Si composition of 70%. The AlSi single crystal substrate 7 was bonded by AuAu bonding and a layer of 10 μm thick GaN single crystal layer 2. The bonding layer 3 has a thickness of 4 μm. A reflective layer pattern 4' is included in the GaN layer 2 near the bonding layer 4 microns. The structure of the reflective layer pattern 4 'cycle 3 m, a bottom diameter of 2 microns, 1 micron high cylindrical Si0 ₂ pattern layer structure.

Claims

Claim

A method of preparing a composite substrate for GaN growth, comprising the steps of:

La) growing a GaN single crystal epitaxial layer on a sapphire substrate;

Lc) bonding the GaN epitaxial wafer bonded to the temporary substrate to a thermally conductive substrate having a melting point exceeding 1000 ° C, and the epoxy-based quick-drying adhesive is carbonized during the bonding process, and the temporary substrate is peeled off, A composite substrate in which a gallium polar face-up GaN epitaxial wafer is bonded to a thermally conductive conductive substrate.

2. The method according to claim 1, wherein step 1) growing a GaN single crystal epitaxial layer on the sapphire substrate, and step lb) transferring the GaN single crystal epitaxial layer from the sapphire substrate to the temporary substrate Then, a metal reflective layer is evaporated on the surface of the GaN single crystal, and then step lc) is performed.

3. The method according to claim 1, wherein in the step lat. GaN epitaxial growth, a layer of GaN is grown, and then a reflective layer material is grown thereon, by photolithography and drying. The etching process prepares the reflective layer material into a micron- or nano-scale periodic structure, and requires exposing the GaN surface at the gaps of the structures, and then continuing to grow the GaN single crystal to a desired thickness, and then performing step lb), The reflective layer material has a refractive index different from that of GaN and has a melting point of 1000 ° C or higher.

The method according to claim 3, wherein the reflective layer material is SiO ₂ or SiN.

5. The method according to claim 1, wherein the sapphire substrate in step la) is a patterned sapphire substrate, and the patterned sapphire substrate is designed according to a structure of a reflective layer in the composite substrate. It is obtained by photolithographic stripping to prepare a microscopic or nanoscale periodic structure pattern on the surface of sapphire.

The preparation method according to claim 1, wherein the bonding method of the step lc) is a rigid bonding or a flexible dielectric bonding, wherein: the rigid bonding is at a temperature of 500 ° C to 900 ° C, pressure The GaN epitaxial wafer bonded to the temporary substrate is directly bonded to the thermally conductive conductive substrate by a thickness of 3 ton / square inch to 10 ton / square inch, and the thermally conductive conductive layer substrate material in the rigid bonding The difference in thermal expansion coefficient from GaN is less than 10%; flexible dielectric bonding is to first deposit the bonding metal on the surface to be bonded, then at a temperature of 200 ° C to 900 ° C, pressure 1 ton / square inch to 5 tons The GaN epitaxial wafer bonded to the temporary substrate is bonded to the thermally conductive conductive substrate under a square inch condition.

7. A method of preparing a composite substrate for GaN growth, comprising the steps of:

2a) growing a GaN single crystal epitaxial layer using a sapphire substrate; 2b) bonding the epitaxial wafer grown on the sapphire substrate to a thermally conductive substrate having a melting point of more than 1000 ° C; 2c) stripping the sapphire substrate by laser lift-off to obtain a GaN with a polar face of nitrogen A composite substrate in which an epitaxial wafer is bonded to a thermally conductive substrate.

8. The method according to claim 7, wherein step 2a) after growing a GaN single crystal epitaxial layer on the sapphire substrate, and then depositing a metal reflective layer on the surface of the GaN single crystal, and then performing step 2b) .

9. The method according to claim 7, wherein in the step GaN epitaxial growth process, a layer of GaN is grown, and then a reflective layer material is grown thereon, by photolithography and drying. The etching process prepares the reflective layer material into a micron- or nano-scale periodic structure, and requires the GaN surface to be exposed at the gaps of the structures, and then continues to grow the GaN single crystal to a desired thickness, and then proceeds to step 2b). The reflective layer material has a refractive index different from that of GaN and has a melting point of 1000 ° C or higher.

The method according to claim 9, wherein the reflective layer material is SiO ₂ or SiN.

The method according to claim 7, wherein the bonding method of step 2b) is rigid bonding or flexible dielectric bonding, wherein: the rigid bonding is at a temperature of 500 ° C to 900 ° C, pressure The GaN epitaxial wafer on the sapphire substrate is directly bonded to the thermally conductive substrate by a van der Waals sheet at a temperature of 3 ton / square inch to 10 ton / square inch, and the thermally conductive conductive layer substrate material and GaN in the rigid bonding The coefficient of thermal expansion differs by less than 10%; the flexible medium bonding is to first vapor-deposit the bonding metal on the surface to be bonded, and then at a temperature of 200 ° C to 900 ° C, a pressure of 1 ton / square inch to 5 tons / square The GaN epitaxial wafer on the sapphire substrate is bonded to the thermally conductive substrate under inches.

The method according to any one of claims 1 to 11, wherein the material of the thermally conductive substrate is selected from the group consisting of alloys of one or more of metals W, Ni, Mo, Pd, Au and Cr. Or an alloy of one or more of these metals with Cu, or a Si crystal, a SiC crystal or an AlSi crystal.